This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-108097, filed Apr. 10, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an ultrasonic diagnosis apparatus for extracting harmonic components generated by nonlinear propagation of the living tissue and the nonlinear response of a contrast medium (microbubbles) from a received signal, and generating an ultrasonic image on the basis of the harmonic components.
Imaging based on harmonic components can substantially narrow a beam as compared with imaging based on fundamental wave components that spread from the center frequency of a transmission ultrasonic wave, and hence can realize high resolution. In addition, a certain sound pressure is required to generate harmonic components, imaging based on harmonic components can reduce side lobes. As a method of imaging harmonic components originating from the tissue, THI (Tissue Harmonic Imaging) is available.
A filter method is a typical method of extracting nonlinear components from a received signal. As a method of extracting harmonic components in a wider band, a pulse inversion method is available, in which two ultrasonic pulses having opposite polarities are transmitted at two rates, and signals received at the respective rates are added to cancel out a fundamental wave component, thereby extracting harmonic components as disclosed in Iwao Abiru and Tomoo Kamakura, xe2x80x9cNonlinear Propagation of Ultrasonic Pulsesxe2x80x9d (Technical Report of IEICE, US89-23, p. 53). This method uses the phenomenon that harmonic components are generated in proportion to the square of a fundamental wave. More specifically, since the phases of fundamental wave components maintain the phase of a transmission ultrasonic wave, the first rate fundamental wave component appears in opposite polarity to the second rate fundamental wave component. Therefore, the fundamental wave components cancel out each other. On the other hand, harmonic components are generated in proportion to the square of a fundamental wave, and hence the first rate harmonic component and second rate harmonic component appear in the same polarity. Therefore, the harmonic components are amplified.
The fundamental wave elimination characteristic of the above pulse inversion method is based on the premise that the tissue serving as a propagation medium is still. If, therefore, a moving organ such as the heart is imaged by the pulse inversion method, the received signal waveform and relative positions (depths) of the received signal changes between the two rates in accordance with the motion of the organ. As a consequence, fundamental wave components are left to cause motion artifacts on an image.
It is an object of the present invention to eliminate motion artifacts due to the motion of tissue such as the heart, in particular, in an ultrasonic diagnosis apparatus for repeatedly transmitting an ultrasonic wave, extracting harmonic components from a plurality of received signals obtained by the transmission of the ultrasonic wave, and generating images on the basis of the harmonic components.
An ultrasonic diagnosis apparatus includes an ultrasonic probe, a transmitter configured to supply a transmission pulse to the ultrasonic probe to repeatedly transmit an ultrasonic wave to each of a plurality of scanning lines, and a receiver configured to receive echoes of the ultrasonic waves through the ultrasonic probe and obtaining a plurality of received signals for each of the plurality of scanning lines. A displacement estimating means estimates a relative change accompanying a tissue motion between a plurality of received signals associated with each of the plurality of scanning lines. A displacement correcting means corrects the plurality of received signals in accordance with the change detected by the displacement estimating means. A harmonic component extracting means extracts a harmonic component from the plurality of received signals corrected by the displacement correcting means. A display means generates an ultrasonic image on the basis of the harmonic component extracted by the harmonic component extracting means. A monitor displays the image generated by the display means.
According to the present invention, harmonic components can be extracted in a broad band even from moving organs such as the heart, in particular, and high-quality images unique to harmonic images can be provided for clinical sites.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.